In order to anchor the coupling elements to the stringer tape and to prevent their detachment in response to transverse tensions acting upon the closed fastener, it is known to deform portions of the carrier cord--whose diameter substantially exceeds the thickness of the adjoining stringer tape--between jaws of two mold halves in whose cavities the coupling elements are being formed. According to the usual practice, this deformation occurs between shallow depressions of the jaws which in the closed positions of the mold define a generally rectangular recess whose length in the parting plane of the mold halves approximately equals the original cord diameter while its width transverse to that plane is a fraction of that diameter. Such a dimensioning is designed to compress the fibers of the cord in the immediate vicinity of each coupling element, thereby increasing the density and thus the shear resistance of the cord portion embraced by that element for a firmer connection of the latter with the tape. This densification, on the other hand, greatly reduces the extent by which the cord projects from the stringer tape so that even a moderate tension perpendicular to the tape edge, such as that exerted by a slider during closure of the fastener, can detach a coupling element from the cord and thereby from the tape itself.
In my copending application Ser. No. 247,642, filed Mar. 26, 1981 and now U.S. Pat. No. 4,458,391, I have disclosed a method of improving the bond between a molded coupling element and a woven stringer tape by providing the latter with a limited number of thermoplastic warp threads adjoining the carrier cord, these warp threads being interlockingly engaged by and fused to the coupling elements. The carrier cord, secured to the stringer tape by its weft threads, is thus partly relieved of the task of holding the coupling elements in place.